The problem of treating wastes has been crucially posed for about ten years. Indeed, the majority of the wastes were, in the past, simply deposited in dumps, and therefore no real management of these wastes was carried out.
But now, changes in the nature and amount of wastes have led to adopting an industrial approach in order to carry out their treatment.
Numerous technologies are thus applied for treating wastes so that development may continue without being harmful to the environment. These high performance technologies for destroying wastes have in common that they comprise both a method for destroying the wastes, treatments of the fumes produced during this destruction and management of the liquid or solid residues which are possibly obtained.
Generally, thermal methods for destroying wastes are used in order to overcome the problem posed by the stability of many chemical compounds. Thus, installations for destroying dangerous products are traditionally incinerators, in which, for example, liquid products are mixed with solid products in order to be burned.
However by incinerating the wastes, volatile residues are obtained which further need to be removed.
Moreover, these installations require sizeable volumes for allowing complete reactions between the fuel and the comburent, oxidizer and for reducing operational costs.
In order to find a remedy to these drawbacks, many methods for destroying wastes use plasma technologies. Indeed, methods applying a plasma have the advantage of allowing reduction in the size of the required installations since plasma incinerators give the possibility of attaining very high temperatures and of therefore accelerating the chemical reactions for destroying the wastes and for recombining the thereby obtained chemical elements.
In document [1], efforts are made for destroying organic products by means of a blown arc plasma. The gases from the combustion of the wastes are mixed with air, water or oxygen at the outlet of the plasma torch in a segmented tubular stage. This technique allows destruction of gas wastes in an easy way by mixing the wastes with the plasma gas from the arc torch. Nevertheless, the efficiency of the method is reduced because the feeds to be destroyed do not pass into the torch. Destruction of liquid products proves to be more complicated since it is difficult to homogeneously mix a liquid phase in a gas phase at a high temperature and at a high speed from a blown plasma arc torch. This difficulty further reduces the thermal yield and efficiency of the method.
Another example of the use of blown arc plasmas is shown in documents [2] and [3]. The wastes to be destroyed are introduced into a tubular torch with a blown arc plasma after having been subjected to a change of state into a gas phase by means of an initial burner.
In the technique discussed in document [2], the fact of vaporizing the feed in order to have it pass into the plasma torch, gives the possibility of both increasing the destruction efficiency of the method and considerably complicates the method, since it imposes constant monitoring of proper vaporization of the feed. Addition of a gas burner, which requires a substantial air supply in order to operate properly, leads to a large gas flow rate in which the mass proportion of the feed is reduced.
The method described in document [3] allows introduction of the feed to be destroyed, whether it be liquid or gaseous, directly into the plasma torch. This method uses the technology for stabilizing the electric arc in the torch by means of an electromagnetic field. As this method is a substantial consumer of electrical energy, it is reserved to destruction of products present in a very large amount. Further, no mention is made of the type of gas used for operating the torch or for controlling atomic recombinations. Thus, this method carries out destruction of the products by pyrolysis, i.e. without any oxygen supply, which leads to strongly reducing gases being obtained which have to be burned at the outlet of the torch before being discharged into the atmosphere.
In document [4], the wastes are mixed with water or with methanol and are introduced into a tubular arc torch. Oxygen, instead of air is also used as a plasma gas. The purpose of these modifications is to improve the efficiency of destruction of the wastes. In this document, a tubular segmented arc torch is used. This is a relatively uncommon technology which requires good knowledge of plasma technology in order to define stable operating parameters. The use of two phases, a liquid and gas phase, in this type of technology does not facilitate the establishment of stable operation.
In document [5], a plasma burner is used for purifying and cleaning up gases flowing out of a conventional incinerator. High temperature post-combustion with injection of air in the mixing chamber with gas products to be neutralized is thereby achieved. Again, with this method, the plasma torch is used as an extra energy carrier for purifying gases. Therefore, it is not possible to treat liquids directly without having vaporized them beforehand in a conventional incinerator for example.
Moreover, the fact of not introducing the feed within the torch, for material incompatibility reasons, strongly reduces the efficiency of the method.
It is also possible to use radiofrequency or high frequency plasmas. For example, in document [6], the solid products to be destroyed are first introduced into a rotary kiln so as to be transformed into a gas form. The gas flow is then directed towards a collector where it is mixed with a carrier gas and optionally with liquid wastes. This mixture is then introduced into a high frequency plasma torch. The products from the torch then pass into a centrifuge provided with a toric system for generating electric and magnetic fields. With this system, it is then possible to separate the different elements.
This technique has as a primary purpose, the separation of the different constituents of feeds with optional recovery of recyclable valuable products such as heavy elements.
The torch has a particular geometry into which the feeds are introduced via an undefined collector. The attained field temperatures which are from 300 to 1,000° C. do not allow destruction in the strict sense of the term but rather allow conditioning for separation of the different elements.
Document [7] relates to the destruction of toxic gas products of military origin by means of a plasma torch operating under an air/argon mixture.
At the outlet of the torch, an air/water quenching mixture is introduced in order to stop the reactions. The feeds to be destroyed either pass into an inerting module, or into the plasma module. Thus, it appears that it is mainly the gases that are directed towards the plasma module. The introduction of liquid is only a possibility depending on the composition of the feed.
Most methods for destroying wastes as described above use plasma arc torches which are positioned in specific reactors and for which the waste destruction efficiency is insufficient.
This is why, in order to substantially improve these destruction efficiencies, a method was developed in which a liquid or powdery organic or organo-halogenated compound to be destroyed is mixed with water and introduced with a plasma-forming gas into the core of an inductive plasma torch. In other words, this method is based on the use of an induction plasma torch into the inside of which the feed of compounds to be destroyed is introduced. This method ensures destruction of the feed by introduction of water which is sprayed into the plasma with the compounds to be destroyed.
This method is described in document FR-A1-2866414 (8) and the device for its application is illustrated in FIG. 1.
This device comprises an induction plasma torch supplied with a plasma gas (1) ionized by means of an inductor (2) in order to thereby form a plasma (3).
This torch is equipped upstream with a system (4) for introducing the feed to be treated. In order to ensure compliant destruction of the feed, water is mixed with the introduced feed (5).
Dissociation of water at a very high temperature ensures the oxygen supply required for oxidizing the organic or organo-halogenated species on the one hand and a hydrogen supply required for forming HCl on the other hand.
The first claim of document [8] indicates on this matter that the organic product is mixed with water in a sufficient amount in order to at least satisfy the stoichiometric ratios between the carbon and oxygen atoms of the mixture, or that the organo-halogenated product is mixed with water in a sufficient amount in order to at least satisfy the stoichiometric ratios between the carbon and oxygen atoms of the mixture on the one hand, and between the hydrogen and halogen atoms of the mixture, on the other hand.
Indeed, a lack of hydrogen in the medium may be at the origin of the production of undesirable molecules such as phosgene COCl2. The plasma (3) generates many highly reactive ionic species which ensure the destruction of the organic compounds. These destruction reactions occur in the reactor (6) which is maintained at a very high temperature thanks to refractory materials (7) which line its internal walls (8).
Introduction of air and/or oxygen (9, 10) at the bottom of the reactor and at a venturi (11) ensures significant mixing of the gases and an additional supply of oxygen.
Next, the gases are rapidly cooled before entering a recombination area (12) in which the last reactions occur.
The gases are then directed (13) towards a treatment notably consisting in neutralization of the acid species.
A pilot installation was set into place in order to test the efficiency of the method described in document [8]. The power of the plasma generator is 4.5 kW for an effective power in the plasma from 1 to 1.5 kW.
If degradation of the products is very satisfactory, the energy efficiency of the method may be described as average or even poor, because of the large amount of water to be heated and to be volatilized.
Two reference molecules, taken as an example, were treated in the pilot installation in which they were each supplied at a rate of 100 g/h:                trichloromethane or chloroform of formula CHCl3,        chlorobenzene of formula C6H5Cl.        
Treatment of chloroform requires a water supply of a minimum of about 30 g/h for a treatment heat balance of about 100 W. The power available in the torch is thus widely sufficient for ensuring complete treatment of the solvent.
Treatment of chlorobenzene requires a water supply of a minimum of about 200 g/h for a treatment heat balance of about 550 W. If the power in the plasma is still sufficient, the available margin is more limited. If the amount of water is brought to twice the stoichiometry for securing, guaranteeing the treatment, the heat balance increases to approximately 900W which reduces the energy margin to almost 0.
Being aware that for reasons of reaction efficiency, it is reasonable to work with at least double water stoichiometry, the energy yield is widely reduced.
As an illustration, FIG. 2 illustrates the time-dependent change in the maximum treatment flow rate of an aliphatic chlorinated solvent CxHyCl per available kW in the plasma.
It should be noted that the calculations were carried out with solvents comprising aliphatic chains with a single chlorine atom (z=1). But the conclusions would be identical with a number of chlorine atoms z different from 1.
It appears that this flow rate substantially decreases with the number of carbon atoms x, which makes the method moderately or not very attractive for a large scale industrial application.
From the foregoing, it therefore emerges that the method and the device which are described in document [8] have certain drawbacks which are notably the following:                an insufficient energy yield of the method;        a limited feed rate;        the use of a costly plasma gas such as argon which makes the method not very interesting within the scope of an industrial application;        difficulties for treating and destroying compounds which are non-miscible with water.        
Therefore, there exists a need for a method and a device for destroying a feed comprising at least one organic compound by means of at least one induction plasma formed by at least one plasma-forming gas ionized by an inductor, which do not have the drawbacks of the method and of the device described in document [8].
The goal of the present invention inter alia is to provide a method and a device for destroying a feed comprising at least one organic compound by means of at least one induction plasma formed by at least one plasma-forming gas ionized by an inductor which inter alia meet this need.
The goal of the present invention is further to provide such a method and such a device which do not have the drawbacks, defects, limitations and disadvantages of the methods and devices of the prior art such as the method and the device described in document [8].